Single phasing preventor



J. R. WAL-row ET AL 2,749,4@7

SINGLE PHSING PREVENTOR June 5, i956 2 Sheets-Sheei l Filed Oct. l5,1953 ATTORNEYS jm@ 5 E956 J. R. WALTON ETAL 2,7497

SINGLE PHASING PREVENTOR Filed Oct. l5, 1953 2 Sheets-Sheet 2 Fie? FIGATTORNEYS SINGLE PHASNG PREVENTR lames Rignell Walton, Harpenden, .lamesNeil Burke, Barnet, and Arnold Walton Cure, St. Albans, England,assignors to The Electrical Apparatus Company, Limited, St. Albans,England, a company of Great Britain Application Gctober 15, 1953, SerialNo. 386,352

8 Claims. (Cl. Z130- 116) This invention relates generally to devicesfor protecting polyphase circuits.

Devices of the subject type are especially useful for protectingpolyphase alternating current electrical apparatus, and particularlypolyphase electric motors, and comprise a plurality of current-sensitivemembers each of which can respond to one of the currents between whichunbalance is to be avoided, a switch, and a operative connection betweenthe current-sensitive members and the switch for operating the latter todisconnect the apparatus by non-uniform movement of the member in theevent of unbalance, Since the device is particularly useful inprotecting polyphase motors against single phasing, it is describedhereinafter as a single phasing preventor or more brielly, as apreventor. According to the practice of the prior art, a number ofbimetal strips was employed to operate the preventor, these being heatedin accordance with the currents in the respective phases of the circuitbeing protected, either by passing current through the bimetal itself orthrough a resistance element mounted with it. In either case, if it wasdesired to renew the heating elements, or to exchange them for others ofdifferent value, it was necessary to reassemble the bimetal strips, ifnot to exchange them for others, which involved re-adjusting themechanism.

Therefore, it is the primary object of the present invention to providefor the replacement of the heating elements without interference withany mechanically operated parts, whereby to obviate the necessity forre-adjustment when the heating elements are replaced. in accordance withsaid object, it is a more specic object to provide for the replacementof the heating elements without disturbing the bimetal strips. Anotherobject of the present invention is to make the means of attaching inplace the heaters, or carriers, therefor such that positive location isobtained on interchange.

A further object is to provide a more efiicient improved and generallysimplified single phasing preventor.

The above and other objects, features and advantages of the presentinvention will be more fully understood from the following descriptionconsidered in connection with the accompanying illustrative drawings.

In the drawings:

Fig. 1 is a top plan View of a preventor, pursuant to the presentinvention, for protecting a three phase electric circuit againstunbalance, two of the heaters being removed for purposes ofillustration;

Fig. 2 is a view similar to Fig. l, with the cover of the deviceremoved, two of the heaters being removed as in Fig. l;

Fig. 3 is a front elevation taken in the direction of arrow 3 in Fig. 1;

Fig. 4 is a sectional view taken on the line 4-4 of Patented June 5,i956 Figs. 7 and 8 illustrate one form of heater for the preventor; and

Figs. 9 and 10 illustrate another form of heater therefor.

Referring now to the drawings in detail, the protector device of thepresent invention is provided with an insulating base 2l) on which thevarious component parts thereof are mounted. Provision is made for threelaterally spaced conducting brackets or terminal elements 22, eachprovided with a terminal 24 for the incoming current, said bracketsbeing suitably secured to the base 20, as by the securing elements 23(Fig. 4). Three conducting brackets or terminal elements 26 are alsosecured to the base 20 as by the securing elements 27, said bracketsextending through apertured portions 29 of the base and being eachprovided with a terminal Z8 for the outgoing current. Consequently, itwill be understood that there is an input terminal 24 and an outputterminal 23 for each current phase. The base 20 has defined thereinthree laterally spaced chambers 34 in each of which there is mounted abimetal strip 39. More specifically, each strip is provided with alooped portion 32, an end portion 33 which is secured to the insulatedbase in the companion chamber, as by means of a clip 36, and with a freeend 38 which extends from the chamber and engages in slots 40 and 42provided in the longitudinally extending slide members or plates 44 and46, respectively. The plates are disposed between the base 2G and acover 48 which is ixed thereto, said base and cover dening a housing forthe protector. Said plates are mounted for slidable movement in thedirection of their longitudinal axis under the control of the birnetalstrips. Adjacent one end thereof, the upper plate 44 carries a pivot 5t)on which there is pivotally mounted a bell crank lever 52. A pin 56carried at one end of the lower plate 46 extends into and is connectedwith one arm 54 of the bell crank lever. The other arm 58 of the bellcrank lever engages a hook contact 60, which constitutes one of thecontacts of a switch 61, best illustrated in Fig. 6, the other switchcontact being indicated at 68.

Switch 61 is of similar construction and operation to the switchillustrated and described in the British patent specification No.553,154 and in No. 628,220. As illustrated and described therein, and asshown herein, the aforementioned hook contact of the switch extendsvthrough an opening 62 provided in a fixed conducting bracket 64, whichis provided with a terminal screw 65 (Fig. 5). One end of the companioncontact 68 is hooked, as at 7i), into a contact bar 72 (Fig. 3) which isfixed to the device in a suitable manner and which is provided with aterminal 76. A spring '74 operates to move the contact 68 downwardlyfrom the full line, to the broken line position thereof, as illustratedin Fig. 5, when the companion contact 60 is rocked in a clockwisedirection, viewing said figure. In this connection it will be noted thatthe hook contact 60 has an extension portion 66 upwardly of the bracket62, which extension is biased by a spring 67 in a direction to effectengagement of the opposite end of the hook contact 6i) with thecompanion contact 68. It will be understood that the switch contacts 60and 68 are connected in well known manner to control the supply ofcurrent to a suitable load, for example, and not by way of limitation,to a motor, and, when the switch is opened, protects the motor bycutting off the current supply thereof. In this connection, the switchmay be connected in series with the operating coil of a suitablecontacter (not illustrated) for controlling the supply of current to theapparatus, for example, a motor, which is being protected.

The aforementioned spring 67 serves to press the hook contact 6d againstthe bell crank lever 52, as best illustrated in Figs. 3 and 5. When thebell crank lever is in the position thereof illustrated in Fig. 3, thehook at the lower end of the hook contact 60 is in contact with andholds the companion switch Contact or arm 68 ot the switch 6l. FEheVpressure yexerted :by the spring 67 through the hook contact 66 on thebell crank 52, makes the latter thrust the plate d6 in the direction ofthe arrow 47 in Fig. 3, and relative to the companion plate d4, so taras such movement is permitted by the engagement of the bimetal ends 33in the slots of these plates. The relative position of the various partsbeing, as illustrated in Fig '5. Uniform hearing of the bimetal stripsSti will cause their tree e, 33 to move in the direction of the arrow d?by equal amounts, and it will be apparent that the plates lid and d()and the bell crank lever 52 will move in the direction of said arrow i7with said free ends of tie heaters. The upper arm 53 of the bell cranklever, ag 'nst which the hook contact o@ presses, will slide under thelatter without affecting the closed condition of the switch di. Hou#ever, should unequal heating ot the him-etal st s occur, so that one ofthem moves less than the others, this one will limit thc movement of theplate do in the direction ot the arrow d?, but the plate dd willcontinue to move in said direction under pressure from the other stripswhich are moving further than said one strip. Consequently, the platewill move in the direction of the arrow i7 over plate d6, carrying withit the pivot t? of the l crank lever 52, while the piu 5o which is hiredto the ate de and which engages in the lower arm 54 of the l crank leverwill prevent that lower arm from moving in the direction of the arrow47. Consequently, the bell crank lever will pivot in a counter-clockwisedirection, viewing Fig. 3, so that the arm 5S thereof moves upwardlyfrom the position thereor" illustrated in said ligure. This arm forcesthe hook Contact dit upwardly, viewing Fig. 3, until it disengages thecompanion switch contact 68, permitting the latter to be moved to theopen position thereof by spring 74, as illustrated in broken line inFig. 5. Since, as previously indicated, the switch is connected tocontrol the supply of current to a motor, it will be apparent that whenopened the switch protects the motor by cutting oit the supply ofcurrent thereto. As previously indicated, the Contact arm d8 beingpivoted at the hook portion 7@ and biased by the spring '7dto pressfirmly against the 'nook end of hook contact 7) iu the engaged conditionthereof, when the lower portion ot the hook Contact di) is moved in thedirection of the arrow 63 (Fig. 6) to disengage the hooked end there-offrom the companion contact 68, as previously explained, the latter ismoved downwardly by the spring 7d until it abuts an insulating nose 78,as illustrated in Fig. 5.

Once the switch 'Si is opened in the described manner, it remains openeven though the hook Contact dit moves back in the direction oppositethe arrow o3. However, alter the hook Contact has returned to theposition thereof illustrated in Fig. v5 or 6, the companion switchcontact (itt may be re-enoaged therewith by moving upwardly upon thenose as illustrated in Fig. 5, to move the contact back into engagementwith the hook Contact all to reset the switch.

lrovision is made for a bracket titi which is pivoted at d2 whichcarries a bimetal strip S4. Provision is also made for a lever do whichis pivotally mounted, as at S3, and which is provided with a pointer(Fig. 3), which pointer moves relative to notches @l provided on thebase Zit as the lever 86 is rotated on its pivot. As best seen iu 2, thelover 36 is provided with a projection SM which limita the rotation of'the bracket tit), it being noted that the latter is provided with apart 3l which is adapted to engage the projection 34, said projectionbeing disposed in the path of movement of the part til. As best seen inFig. 3, the bimetal strip tid extends from the bracket 8 into the pathof movement of the lower plate 16 in the direction of the arrow 47 tolimit the movement of said plate in said direction.

En view of the foregoing, it will be apparent that the extent ct' themovement ofthe plate d6 in the direction of the arrow t7 may bepredetermined by the setting of the pointer 9) at a particular ,notch92., the setting of said pointer determining the position of the lever86 and thereby ,limiting the clockwise rotation of the bracket 80,viewing Fig. 2, which in turn determines the setting of the bimetal 8dwhich, as indicated, predetermines the extent of the movement of theplate 46 in the direction of the arrow 67. Under conditions of uniformheating of the various bimetal strips 39, the plates 44 and 46 move inthe direction of the arrow 47, viewing Fig. 3, as previously d bed,until movement of the plate 46 is stopped by its engagement with thebimetal strip tid. Further heating of the strips 3) will cause thecompanion plate 44 to move in the direction of the arrow 47, relative tothe plate 46, to result in the pivotal movement of the bell crank leverin a direction to open the switch 6l, as previously described, andthereby discontinue the supply of current to the apparatus, 'for examplea three phase motor which is being protected. Therefore, it will beapparent that the preventor device herein described provides protectiongaiust ordinary overload of the ap aratus as well as protef ion againstunhalanee in the various current phases thereof. ,Ev a suitable designor construction of the bimetal strip Se, so that .for a given change ofambient temperature its delection is the .same as that of the bimetalstrips 3h, the uniform overload which will trip the switch 67, caused tobe made independent of ambient temperature.

The base Ztl and the cover 48, which constitute the housing, areextended to overlap the free ends 38 of the birnetal strips Sti to holda transparent front window plate (Fig. 2). The base and the cover mayalso be extended at each side of the device to overlap the strip andassociated parts, and to hold transparent side window plates and liftil.Consequently, the various operating parts are clearly visible and yetthey are protected. in this connection, it will be understood that it isparticularly useful to be able to observe the movement of the free ends33 of the various strips 3l) in order to see if they are movingtogether, as when the three leads of the circuit being protect-ed areequally loaded, or if one or more of the ends is lagging, as whenimbalance exists between the three leads of rthe circuit beingprotected.

Cover 425, when mounted on the base 2l), closes the top of the variouschambers 34. The heaters MEZ are disposed in each of the chambers 34when the protector device is in use. Pursuant to the present invention,as best shown in Fig. 4, each heater M92 is fixed to a companionincoming terminal bracket 22 by a securing portion lii which extendstransversely of the bimetal loop outwardly of the associated chamber,through the medium ot the screw 1194 and is iixed to a companionoutgoing terminal bracket 26 by a securing portion 105 which extendstransversely of said loop outwardly ofthe associated chamber, throughthe medium of a screw 106. Consequently, it will be apparent that atboth ends thereof, the heater is secured outwardly of the housing. Itwill be noted from the left hand. chamber, viewing Fig. 2, that theheater lies within and adjacent to the loop 32 of the associatedbirnetal strip 3@ in close spaced thermal relation therewith to obtainmaximum heat transfer. Referring now to Fig. 4, it will be noted thatthe housing cover d3 is cut away, as at 198, to permit the heater to bereadily removed or replaced through the cover, without the necessity ofremoving the latter, by merely removing the screw ldd and by backing upor slackening the screw 106. Each heater 102 has attached to itself, ormade a part thereof, a plate llt) which serves to close the opening 108provided in the cover 48 when the heater is in position in the device.Fig. 2 illustrates only one ot the heaters in position, the heater inthe left hand chamber, viewing said tigure, being shown in section atthe level of the companion bimetal strip 30, the heaters in the centerand the right hand chambers having been removed for purposes ofillustration. The center and right hand heaters have also been removedfrom Fig. 1 and in addition the screws 104 which hold the heaters to thebrackets 22 have also been removed so as to reveal the openings 108 inthe top cover 48.

The heater 102 shown in position in the protector device is formed ofsheet metal and is suitably shaped for disposition within the loop 32 ofthe associated bimetal strip and to provide the terminal connectingportions 103 and 105 thereof. Thicker or thinner sheet metal is employedfor larger or smaller currents respectively, provided however that theheater is not made of such thin material as to be readily liable toaccidental deformation.

For smaller currents, a heater 102A, as illustrated in Figs. 7 and 8 maybe used. Said heater is made of spirally wound wire, being provided withthe apertured end portion 112, apertured as at 112A, for connection byscrew 104 to the terminal brackets 22 and with the U-shaped end orperipherally interrupted portion 114 for connection by screw 106 to theterminal bracket 26. For still smaller currents, a heater 102B, asillustrated in Figs. 9 and l0 may be used. Said heater is formed of arelatively thin or ne wire which is spirally wound on an insulatingformer or mounting member 116. The heater 102B is provided with anapertured end 118, apertured as at 118A, for connection by screw 104with the terminal bracket 22 and with a slotted end 120 for connectionby screw 106 to the terminal bracket 26. It will be understood that theheater 102 is also apertured in the connecting portion 103 thereof, andis slotted in the connecting portion 105 thereof in the same manner, asat 120 in Fig. 9. lt will be noted in addition, that the U-shapedopening 114 in Fig. 7, is substantially in the form of an open endedslot as in Fig. 9. Therefore, in view of the slotted ends of each of theheaters, in removing or replacing a heater, the screw 106 which engagesin said slotted ends needs to be slackened back only. However, the screw104 must be entirely removed, but being at the top of the device, aswill be apparent from Fig. 1, this is readily effected, and, in order tofacilitate the removal of the screw 104, the latter is provided with along hexagon head to provide a suitable iinger grip. Once the screw 104is entirely withdrawn, and the screw 106 is partially withdrawn, theheater may be readily removed through the opening 108 in the cover 48without the necessity of removing the cover. If the heaters are notinherently suiiiciently rigid, strict interchangeability may be securedby mounting the heater on a carrier which may be of ceramic or otherheat resisting material; moreover all the heaters may be mounted on onecarrier, or the carriers of different phases mounted together to formone unit. In any event, the attaching means for the heaters, or carriersif used, as previously described, provide for positive location of thevarious heaters upon interchange or replacement thereof.

In view of the foregoing, it will be readily apparent that there is nodirect mechanical connection, nor any electrical connection whatsoever,between the heaters and the adjacent bimetal strips 30. On removing onlyone screw, namely the screw 104, and on slackening or backing up anotherscrew, namely the screw 106, a heater may be removed and may be replacedby another heater without disturbing any of the operating mechanism ofthe device or the associated bimetal strip.

While we have shown and described the preferred embodiments of ourinvention, it will be understood that various changes may be made in theidea or principles of the invention within the scope of the appendedclaims.

Having thus described our invention, what we claim and desire to secureby Letters Patent is:

l. In a protective device for electric circuits, operating mechanism forsaid device including a circuit controlling switch, a plurality ofthermally responsive elements and means for operating said switch inresponse to the condition of said elements; heaters for said elements,respectively, energized by the currents in said circuits, respectively,and means for removably mounting said heaters in said deviceindependently of said operating mechanism, whereby said heaters arereplaceable without interference with said operating mechanism, saidthermally responsive elements being flexible bimetal members, and saidheaters each being mounted in spaced thermal relation with an associatedbimetal member and independently thereof, said bimetal members eachhaving a loop defined therein and each heater being mounted within theloop of its associated bimetal member.

2. In a protective device for electric circuits, operating mechanism forsaid device including a circuit controlling switch, a plurality ofthermally responsive elements and means for operating said switch inresponse to the condition of said elements; heaters for said elements,respectively, energized by the currents in said circuits, respectively,and means for removably mounting said heaters in said deviceindependently of said operating mechanism, whereby said heaters arereplaceable without interference with said operating mechanism, saidthermally responsive elements being flexible bimetal members, and saidheaters each being mounted in spaced thermal relation with an associatedbimetal member and independently thereof, said bimetal members eachhaving a loop dened therein and each heater being mounted within theloop of its associated bimetal member, said mounting means includingspaced terminal elements for each circuit and each heater havingsecuring portions extending outwardly of its associated loop forremovable securement to the associated terminal elements.

3. In a protective device for electric circuits, operating mechanism forsaid device including a circuit controlling switch, a plurality ofthermally responsive eiernents and means for operating said switch inresponse to the condition of said elements; heaters for said elements,respectively, energized by the currents in said circuits, respectively,and means for removably mounting said heaters in said deviceindependently of said operating mechanism, whereby said heaters arereplaceable without interference with said operating mechanism, saidthermally responsive elements being flexible bimetal members, and saidheaters each being mounted in spaced thermal relation with an associatedbimetal member and independently thereof, said bimetal members eachhaving a loop dened therein and each heater being mounted within theloop of its associated bimetal member, said mounting means includingspaced terminal elements for each circuit and each heater havingsecuring portions extending outwardly of its associated loop forremovable securement to the associated terminal elements, and securingmembers threadedly engageable in said terminal elements for releasablysecuring said heater portions thereto, respectively, one of said heaterportions being peripherally interrupted, whereby said one heater portioncan be disconnected from its associated terminal element withoutdisengaging the associated securing member from said latter terminalelement.

4. A protective device for electric circuits comprising a housing forsaid device, a plurality of chambers defined in said housing, operatingmechanism in said housing responsive to unbalance in said circuits andincluding thermally responsive elements for said circuits, respectively,said elements being mounted in said chambers, respectively, and heatersfor said elements disposed within said chambers, respectively, in spacedthermal relation therewith and being removably mounted in operativedisposition outwardly of said chambers, and means for mounting saidheaters externally of said housing, said means comprising spacedterminal elements for each circuit provided with portions disposedoutwardly of said housing, said heaters interconnecting the associatedterminal elements by releasable securement to said portions thereof,said device being further characterized in that the heaters are sheetmetal members provided with secur- ,uy ing portions extending outwardlyof said housing, and securing elements interconnecting associatedterminal and heater portions, one of said portions in each heater beingperipherally interrupted, whereby to facilitate the disconnection ofsaid one heater portion from its associated terminal portion withoutremoving the securing elcment from the latter.

5. A protective device for electric circuits comprising a housing forsaid device, a plurality of chambers dened in said housing, operatingmechanism in said housing responsive to unbalance in said circuits andincluding thermally responsive elements tor said circuits, respectively,said elements being mounted in said chambers, respectively, and heatersfor said elements disposed Within said chambers, respectively, in spacedthermal relation therewith and being removably mounted in operativedisposition outwardly of said chambers, and means for mounting saidheaters externally ot said housing, said means vcomprising spacedterminal elements for each circuit provided with portions disposedoutwardly of said housing, said heaters interconnecting the associatedterminal elements by releasable securement to said portions thereof,said device being further characterized in that the heaters are spirallywound elements provided with securing portions extending outwardly ofsaid housing, and securing elements interconnecting associated terminaland heater portions, one ot said portions in each heater being 5.5-shaped, whereby to facilitate the disconnection of said one heaterportion from its associated terminal portion without removing securingelement from the latter.

6. A protective device for electric circuits comprising a housing .forsaid device, a plurality of chambers defined in said housing, operatingmechanism in said housing responsive to unbalance in said circuits andincluding thermally responsive elements for said circuits, respectively,said elements being mounted in said chambers, respectiveiy, and heatersfor said elements disposed within said chambers, respectiveiy, in spacedthermal relation therewith and being removably mounted in operativedisposition outwardly of said chambers, and means for mounting saidheaters externally of said housing, said means comprising spacedterminal elements for each circuit provided with portions disposedoutwardly of said housing, said heaters interconnecting the associatedterminal elements by releaseable securement to said portions thereof,said device being further characterized in that the heaters are spirallywound elements provided with securing portions extending outwardly ofsaid housing and securing elements interconnecting associated terminaland heater portions, one of said portions in each heater being an openended slot deined therein, whereby to facilitate the disconnection ofsaid one heater portion from its associated terminal portion withoutremoving the securing element from the latter.

7, A protective device for electric circuits comprising a housing forsaid device, a plurality of chambers defined in said housing, operatingmechanism in said housing responsive to unbalance in said circuits andincluding a circuit controlling switch, a plurality of bimetal stripsfor said circuits, respectively, and means for operating said switch inresponse to the condition of said strips, said means including a pair ofmembers mounted for relative movement, said members having slots definedtherein, said strips being disposed in said chambers and having free endportions extending therefrom and through said slots for eiectingmovement of said members upon ilexing of said strips respectively, andheaters for said strips, disposed within said chambers, respectively, inspaced thermal relation with said strips, said heaters extending fromthe respective chambers and being removably mounted outwardly of saidchambers.

8. A protective device for electric circuits comprising a housing forsaid device, a plurality of chambers deued in said housing, operatingmechanism in said housing responsive to unbalance in said circuits andincluding a circuit controlling switch, a plurality of bimetai stripstor said circuits, respectively, and means for operating said switch inresponse to the condition of said strips, said means inciuding a pair ofmembers mounted for relative movement, said members having slots definedtherein, said strips being disposed in said chambers and having tree endportions extending therefrom and through said slots for effectingmovement of said members upon tlexing ot' said strips respectively, andheaters for said strips, disposed within said chambers, respectively, inspaced thermal relation with said strips, said heaters extending fromthe respective chambers and being removably mounted outwardly of saidchambers, and a transparent window provided in said housing throughwhich the tree ends of said bimetal strips are visible.

References Cited in the tile of this patent UNITED STATES PATENTS1,910,494 OKeete May 23, 1933 2,'r99,477 Besag May 7, 1940 2,495,608Schleicher Jan. 24, 1950 2,506,796 Krieger May 9, 1950 2,58l,882 RandallIan. 8, 1952 2,584,673 Cole Feb. 5, 1952 FOREIGN PATENTS 482,822 GreatBritain Apr. 4, 1938 553,l54 Great Britain May 10, 1943

